A spectroscope is employed for a device for measuring spectral characteristics of substances, such as absorption spectrums and fluorescence spectrums (see non-patent document 1).
A conventional spectroscope employing a prism is shown in FIG. 1. This spectroscope 100 includes a prism 101, which serves as spectroscopic means, a slit plate 102, which serves as wavelength selection means, and a photodetector 103.
A conventional spectroscope employing a diffraction grating is shown in FIG. 2. This spectroscope 200 includes a diffraction grating 201, which serves as spectroscopic means, a slit plate 202, which serve as wavelength selection means, and a photodetector 203.
Referring to FIGS. 1 and 2, wavelength dispersion elements, such as the prism 101 and the diffraction grating 201, are employed as spectroscopic means, and input light is spatially dispersed in directions that differ for individual wavelengths. From the dispersed light, only one portion is extracted by the wavelength selection means, and thus, light having a specified wavelength can be obtained. At such a time, when either the prism 101 or the diffraction grating 201 is mechanically rotated, an arbitrary wavelength to be extracted can be selected.
Furthermore, for an optical communication field, a spectroscope is employed to select a wavelength during signal processing. A conventional spectroscope employing an arrayed waveguide grating is shown in FIG. 3. An arrayed waveguide grating 301 includes an input slab waveguide 303, connected to an input waveguide 302, an output slab waveguide 306, connected to an output waveguide 307, and arrayed waveguides 304, which connect the input slab waveguide 303 and the output slab waveguide 306. A specific length difference between adjacent waveguides is employed for the arrayed waveguides 304, and heaters 305a and 305b are relatively positioned for the individual waveguides.
An optical signal received at the input waveguide 302 is transmitted, via the input slab waveguide 303, and distributed to the arrayed waveguides 304. On the plane of incidence for the output slab waveguide 306, the optical signal is allocated for a different phase that is consonant with the wavelength of the signal. Since the output slab waveguide 306 serves as a collective lens, at the boundary between the output slab waveguide 306 and the output waveguide 307, the optical signal is collected at a different location in accordance with its wavelength. Therefore, only an optical signal having a specified wavelength, which has been collected at the boundary between the output slab waveguide 306 and the output waveguide 307, is output through the output waveguide 307.
At this time, a current is supplied to the heater 305a or 305b, arranged along the arrayed waveguides 304, and a thermo-optic effect is employed to change the equivalent refractive index of the arrayed waveguides 304. When the equivalent refractive index has been changed, the phases of optical signals passing through the arrayed waveguides 304 are shifted. Therefore, when a phase shift is controlled, only an optical signal having an arbitrary wavelength will be output through the output waveguide 307.
Non-patent Document: “The Physics of Light”, Kohji Kushida, Published by Kyoritsu Shuppan Co. Ltd., First edition, Eighth impression, Apr. 15, 1993.